High frequency amplifier



Oct. 3, 1933. B. SALZBERG 1,928,764

HIGH FREQUENCY AMPLIFIER Filed Sept. 17, 1930 INVENTOR BERNARD SM. BERG ATTORNEY Patented 3, 1933 UNITED STATES 1,928,764 men FREQUENCY AMPIJFIER Bernard Sahberg, Rocky Point, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application September 17, 1930 Serial No. 482,397

18 Claims. (CL 178-171) This invention relates to the high frequency electrical art andhas as an object the provision of an amplifier for ultra-short wave length electrical oscillations. g

The ordinary-and well known-methods for obtaining. amplification at the frequency of the incoming signal, make use of an electron discharge device whose control electrode or grid is at a negative potential and whose anode is at a positive (higher) potential with respect to the cathode. The alternating signal voltage is superposed upon the negative polarizing voltage between grid and cathode, resulting in corresponding variations in the velocity and number of electrons which travel'from the hot cathode to the anode. These variations represent alternations of current (of greater magnitude than the control current) in the local, or anode circuit, and resultin similar, and greater, alternations of voltage across the impedance in this circuit.

It is important to note: (a) that the velocity of the electrons which travel from the cathode to the anode is high enough to be safely regarded as being, at the usual signal frequencies, practically infinite; and (by that the capacitance between grid and cathode, of the order of a few micromicrofarads, is usually, at these frequencies, of little concern.

At the shorter wavelengths, however, these conditions no longer obtain, as a few simple calculations will immediately prove.

The'time it takes for an electron to go from cathode to anode may be obtained, for the usual low temperature-cathode tubes, with a fair degree of approximation from the simple formula I exasx 10- f -IOXO-QS 1-3 X10 ICC. v

assuming that the a'nodeis 45 volts positive with respect to the cathode, This time quantity should be small'compared to a half period of the signal wave, so that variations of voltage impressed between the cathode can effect,

v practically similar variations of' current in the anode'circu it',

The period of an alternating E. M. r'. is

(c=velocity of light in vacuo) and for a signal so wave of, say cms. length, the duration of a half cycle is, therefore,

2 3x10" Therefore, not only is t not large compared to t1, but it is even less than that quantity. This condition imposes a definite wave -length limit below which ordinary amplifiers cannot be made to operate successfully.

Another fact of importance resides in the effect of the interelectrode capacitance at these high frequencies. At a wave-length of 60 cms. the reactance of a capacitor,

Jag- I is, even for only 4 micro-microfarads,

This low reactance, shunted across the ordinary type of lumped" circuit, is enough, by itself, to impose a definite lower wave-length limit. I

These limitations are suiilcient to render the ordinary type of radio frequency amplifiers entirely inadequate at wave-lengths below one meter.

Accordingly, the principal object of my invention is the provision of an amplifier, in which the foregoing difficulties have been overcome, which will function successfully at the ultrashort wavelengths. Briefly, to carry it out, I provide for amplification an electron dhcharge device, or a plurality of electron discharge devices, preferablv of cylindrical symmetry, having their anodes at relatively negative or small positive potentials andthe intermediate electrodes at relatively (high) positive potentials with respect to the cathodes. Consequently, by virture of the high intermediate electrode potential, electrons are speeded up in their travel from cathode to anode and are given such an increased velocity relative to the velocities of electrons in ordinary electron discharge devices, that the speed of the electrons within the tube is no longer an objection.

However, polarizing the electrodes of a discharge. device in the manner indicated, tends to the device self oscillatory, an undesirable feature in amplifiers. Accordingly, a further object of my invention is to prevent the self oscillation of the amplifiers used in accordance with this invention. I do so by suitably adjusting the electrode potentials, together with providing means for neutralizing any tendency toward self oscillation.

To reduce the effects of the interelectrode capacitances of the devices, I utilize for tuning purposes closed or short circuited transmission lines, (having slides therein in order to provide -f0r variation of their effective lengths) whose spacing is small, makingtheir capacitance per unit length large compared with that of the devices. Furthermore, as the frequencies dealt with are very high, the lines are placed close together relative to a wavelength in order to make them non-radiating. The use of such transmission lines for tuning, I have found, greatly reduces the effect of the interelectrode capacitance.

In addition, in order to reduce the actual interelectrode capacitance, I prefer to couple pairs of the devices in pushpull fashion and cascade the pairs of pushpull coupled or connected amplifiers. By connecting the amplifiers in pushpull fashion, input interelectrode capacitance is halved and moreover, prevention of feed back and its concomitant singing or self oscillation is easily accomplished. In addition, such pushpull arrangements result in electrical and mechanical symmetry, a desirable feature.

-Although I have defined my invention in the appended claims, it may best be understood both as to its structural organization and mode of operation by referring to the accompanying drawing, wherein Figure 1 is a wiring d agram of a transmitter embodying an amplifier built in accordance with principles of my invention, and

Figure 2 is a wiring diagram of a receiver hav-- described by Nils E. Lindenblad in his copendii g application, Serial Number'486,375, filed ()ctob :r 4, 1930, assigned to the Radio Corporation of America, andit comprises a pair of electron dis- I charge devices 2, 4 having their grids connected together through short circuited transmission line- 6 and their anodes connected together and transmission line 8 to the anodes of the,

devices 2, 4 from a potentiometer 16. The

cathodes of the devices are energized by a suitable source of potential 20, in series with a rheostat 62. In order to start and maintain oscillations, a catalyst element 22, such as described pushpull connected electron discharge devices Transmission line 24' also is terminated by a trombone slide 30, which, of course, short circuits the line and produces standing waves thereon', or, in effect, tunes the line 24 so as to make it efiectively a tuned input circuit supplying energy to the intermediate electrodes 34, 36 of the electron discharge devices 26, 28 respectively.

Tuning, therefore, of the input circuit of theamplifier, and also of the output circuit of the oscillator is accomplished by varying the effective lengths of the transmission lines 24, 8 respectively. I

It should be noted that at the frequencies involved, as the dimensions of the circuits are comparable to the wavelengths, cognizance of the possibility of radiation from the circuits, an effect which is almost always neglected at the longer wavelengths, must be made. For this reason, the spacing between the elements of the transmission lines should be very close compared to the wavelength and this precaution should be observed for both transmitting and receiving circuits, such as shown in Figures 1 and 2. In addition, the tuning system so far described is very practical, and greatly reduces the effect of the interelectrode capacitance, which normally tends to reduce the upper limit of frequencies which can be amplified by electron discharge devices.

The positive polarizing potential, varied by means of potentiometer 38, is fed to the grids or intermediate electrode through the adjustable quarter-wave termination or loop 32. As the quarter-wave termination has a very high impedance, and in the ideal case of no resistance, an infinite impedance at the working wavelength,

it has little or no effect upon the input tuning' line 24.

Self oscillation of the amplifier tubes 26, 28 at parasitic frequencies, may be overcome bysuitable choice of electrode polarizing potentials and by proper structural design of the tube elements.

To insure non-oscillation at-the working frequency', I provide neutralizing capacitive elements 42, 44 in the form of metallic plates coupled capacitively to the tubes 26, 28 respectively, and

cross-connected through conductors 46, 48, ad-

justable in length, to the grids or intermediate electrodes thereof. Inthis manner,-anytendency towards self oscillation is eliminated. Amplifled output energy is taken from the amplifier 'Athrough I mm m line50inturnterminated by asuitable trombone slide 52 having anode potentials fed thereto from a potentiometer 54 througlrlead 56 to the voltage nodal point 58 thereof. A suitable antenna 60 coupled through blocking condensers 62, 64, symmetrically about the voltage nodal point 58 of trombone slide 52,

may beenergized with the high frequency energy for the purpose of radiating the modulated oscillations supplied by amplifier A to any suitable receiver.

In Figure 2, I have illustrated, schematically,

quency energy collected upon a' suitable antenna 70 is fed to the cascaded amplifiers 72, 74 of a type similar to the amplifier A shown in Figure l, and hence, need not be described in too great detail here. Each amplifienas shown in Figure 1, comprises a pair of pushpull connected electron discharge devices having their anodes maintained at negative or small positive potentials, and their intermediate electrodes at relatively (high) positive potentials with respect to the cathodes. The potential sources have been omitted for the sake of simplicity. Coupling between the stages, as

described in connection with Figure 1, is accomplished by means of transmission lines which may not only be terminated by trombone slides for tuning purposes, but may also have intermediate their ends, as illustrated at points '78 and 80, trombone slides for variation in effective line length. Similarly, coupling between the transmission lines need not be inductive but may be, as shown at point 82, capacitive, transmission line 84 being capacitively coupled to the output transmission line of amplifier 74 through suitable blocking condensers symmetrically placed about the voltage nodal point at the termination of the line. Tuning of the input and output circuits is accomplished by means of these adjustable transmission lines, whose length is varied so that the highest voltage consistent with the intrinsic tube capacitance shunts is built up at the electrodes. a

A relatively low frequency translating device such as telephones86 is placed in the output circuit of the detector stage 76, which will give a response according to themodulation of the incoming collected ultra-short wavelength energy, due to the fact that the anode current fiow will quency energy applied to detector 76. The detector '76 may or may not have, as desired, the

cross-connected neutralizers. Although the last stage has been termed a' detector as it contains a translating device, it is clear that the entire cascaded arrangement may be arranged to act as a cascaded low wave rectifier system.

Having thus described my invention, what I claim is:

1. An ultra-high frequency amplifier comprising a plurality of electron discharge devices, means for maintaining the intermediate electrodes of said devices at relatively high positive potentials and the anodes thereof at much lower potentials with respect to the cathodes, and means for cascading the devices together.

2. An ultra-high frequency amplifier coniprising a plurality of pairs of electron discharge devices connected in pushpull fashion, means for maintaining the intermediate electrode ofeach device at a relatively high positive potential and the anode thereof at a much lower potential with respect to the cathode, and means for coupling the'pairs of tubes together whereby energy is fed successively from one pair of tubes to another pair of tubes.

3. An ultra-high frequency amplifier comprisinga plurality of pairs of pushpull arranged electron discharge devices, means for maintaining the intermediate electrodes thereof at relatively high positive potentials and the anodes thereof at v much lower potentials with respect to their as-- sociated cathodes, and high frequency transmission lines for cascading the pairs of tubes together.

4. An ultra-high frequency amplifier comprising a plurality of pairs of pushpull arranged electron discharge devices having their intermediate electrodes ,at relatively high positive potentials with respect to the cathode and their anodes at much lower potentials, high frequency transmission lines for cascading the pairs of tubes together, and slides within the lines for adjusting the effective lengths thereof.

5. An ultra-high frequency amplifier comprising a plurality of electron discharge devices having their intermediate electrodes at relatively high positive potentials with respect to the cathodes and their anodesat much lower potentials, and high frequency transmission lines spaced apart a small'distance relative to the working wavelength in order to prevent radiation for coupling the devices together.

6. An ultra-high frequency amplifier comprising a plurality of pairs of pushpull arranged electron discharge devices having their intermediate electrodes at relatively high positive potentials with respect to the cathodes and their anodes at much lower potentials, and high frequency transmission lines, closely spaced relative to the working wave-length for coupling the pairs of devices together.

7. An ultra-high frequency amplifier comprising a plurality of pairs of pushpull arranged electron discharge devices, means for maintaining the intermediate electrodes of the devices at relatively high positive potentials and the anodes thereof at lower potentials with respect to the cathodes, means for cascading the pairs of devices, and means for preventing self oscillation of said devices.

8. A pushpull ultra-high frequency amplifier comprising a pair of electron discharge devices having their intermediate electrodes maintained at relatively high positive potentials with respect to the cathodes and their anodes at lower potentials and' means for preventing self oscillation of said devices.

9. An ultra-high frequency amplifier comprising a pair of pushpull connected electron discharge devices, means for maintaining their intermediate electrodes at relatively high positive potentials with respect to the cathodes and their anodes at lower potentials, and means for coupling one of said devices to the intermediate electrode of the other device and the other device to the intermediate electrode of the one device for preventing self oscillation thereof.

10. An ultra-high frequency amplifier comprising a pair of pushpull connected electron discharge devices,-means for maintaining their intermediate electrodes at relatively high positive potentials with respect to the cathodes and their anodes at lower potentials, and separate external capacitive elements coupled to the anodes of said devices, the element of one device being connected to the intermediate electrode of the other and vice versa, for preventing self oscillation thereof.

11. An ultra-high frequency amplifier comprising a pair of pushpull connected electron discharge devices, means for maintaining their intermediate electrodes at relatively high positive potentials with respect to the cathodes and their anodes at lower potentials, and separate external capacitive elements coupled to the anodes of said devices, the element of one of 'said devices being connected to the intermediate electrode of the other device and vice versa for preventing their intermediate electrodes at relatively high the pairs of devices together, and slides in the lines for varying the eflective lengths thereof.

13. In combination, a plurality of electron discharge devices, transmission lines closely spaced relative to the working, wavelength coupling the devices together, loops having legs which-are each one quarter wavelength long terminating the lines and means for supplying polarizing potentials through the loops to electrodes of the devices.

:14. In combination, a plurality of pairs of electron discharge devices, arranged in pushpull fashion, transmission lines closely spaced relative to the working wavelength coupling the devices together, means for varying the effective lengths of the lines, separate conductive loops having legs which are each a quarter wavelength terminating the lines and means for supplying polarizing potentials through the loops to electrodes or the devices.

15. A cascaded low wave rectifying system comprising a plurality of electron discharge devices, means Ior maintaining the intermediate electrodes of said devices at relatively high positive potentials and the anodes thereof at relatively low potentials with respect to their associated cathodes, means for cascading the devices together, and a translating device associated with the anode circuit of one of said cascaded devices.

16. A cascaded low wave rectifying system comprising a plurality of pairs of pushpull arranged electron discharge devices, means for maintaining the intermediate electrodes of said devices at relatively high positive potentials and the anodes thereof at relatively low potentials with respect to their associated cathodes, means for preventing self oscillation of the devices, means for cascading the pairs of devices together, and a translating device associated with the anode circuit of one pair of said cascaded devices.

BERNARD SALZBERG. 

